| Neptune trojans (selection)|
· 2001 QR322
· 2005 TN53
· 2007 VL305
| Plutinos |
Neptune trojans are bodies that orbit the Sun near one of the stable Lagrangian points of Neptune, similar to the trojans of other planets. They therefore have approximately the same orbital period as Neptune and follow roughly the same orbital path. Twenty-two Neptune trojans are currently known, of which 19 orbit near the Sun–Neptune L4 Lagrangian point 60° ahead of Neptuneand three orbit near Neptune's L5 region 60° behind Neptune. The Neptune trojans are termed 'trojans' by analogy with the Jupiter trojans.
The discovery of 2005 TN53 in a high-inclination (>25°) orbit was significant, because it suggested a "thick" cloud of trojans (Jupiter trojans have inclinations up to 40° ), which is indicative of freeze-in capture instead of in situ or collisional formation. It is suspected that large (radius ≈ 100 km) Neptune trojans could outnumber Jupiter trojans by an order of magnitude.
In 2010, the discovery of the first known L5 Neptune trojan, 2008 LC18 , was announced. Neptune's trailing L5 region is currently very difficult to observe because it is along the line of sight to the center of the Milky Way, an area of the sky crowded with stars.
In 2001, the first Neptune trojan was discovered, 2001 QR322 , near Neptune's L4 region, and with it the fifth known populated stable reservoir of small bodies in the Solar System. In 2005, the discovery of the high-inclination trojan 2005 TN53 has indicated that the Neptune trojans populate thick clouds, which has constrained their possible origins (see below).
On August 12, 2010, the first L5 trojan, 2008 LC18 , was announced. It was discovered by a dedicated survey that scanned regions where the light from the stars near the Galactic Center is obscured by dust clouds. This suggests that large L5 trojans are as common as large L4 trojans, to within uncertainty, further constraining models about their origins (see below).
It would have been possible for the New Horizons spacecraft to investigate L5 Neptune trojans discovered by 2014, when it passed through this region of space en route to Pluto. Some of the patches where the light from the Galactic Center is obscured by dust clouds are along New Horizons's flight path, allowing detection of objects that the spacecraft could image. 2011 HM102 , the highest-inclination Neptune trojan known, was just bright enough for New Horizons to observe it in end-2013 at a distance of 1.2 AU. However, New Horizons may not have had sufficient downlink bandwidth, so it was eventually decided to give precedence to the preparations for the Pluto flyby.
The orbits of Neptune trojans are highly stable; Neptune may have retained up to 50% of the original post-migration trojan population over the age of the Solar System. L5 can host stable trojans equally well as its L4. Neptune trojans can librate up to 30° from their associated Lagrangian points with a 10,000-year period. Neptune trojans that escape enter orbits similar to centaurs. Although Neptune cannot currently capture stable trojans, roughly 2.8% of the centaurs within 34 AU are predicted to be Neptune co-orbitals. Of these, 54% would be in horseshoe orbits, 10% would be quasi-satellites, and 36% would be trojans (evenly split between the L4 and L5 groups).Neptune's
The unexpected high-inclination trojans are the key to understanding the origin and evolution of the population as a whole. L5 and L4 trojans indicates that there was no gas drag during capture and points to a common capture mechanism for both L4 and L5 trojans. The capture of Neptune trojans during a migration of the planets occurs via process similar to the chaotic capture of Jupiter trojans in the Nice model. When Uranus and Neptune are near but not in a mean-motion resonance the locations where Uranus passes Neptune can circulate with a period that is in resonance with the libration periods of Neptune trojans. This results in repeated perturbations that increase the libration of existing trojans causing their orbits to become unstable. This process is reversible allowing new trojans to be captured when the planetary migration continues. For high-inclination trojans to be captured the migration must have been slow, or their inclinations must have been acquired previously.The existence of high-inclination Neptune trojans points to a capture during planetary migration instead of in situ or collisional formation. The estimated equal number of large
The first four discovered Neptune trojans have similar colors.They are modestly red, slightly redder than the gray Kuiper belt objects, but not as extremely red as the high-perihelion cold classical Kuiper belt objects. This is similar to the colors of the blue lobe of the centaur color distribution, the Jupiter trojans, the irregular satellites of the gas giants, and possibly the comets, which is consistent with a similar origin of these populations of small Solar System bodies.
The Neptune trojans are too faint to efficiently observe spectroscopically with current technology, which means that a large variety of surface compositions are compatible with the observed colors.
In 2015, the IAU adopted a new naming scheme for Neptune trojans, which are to be named after Amazons, with no differentiation between objects in L4 and L5.The Amazons were an all-female warrior tribe that fought in the Trojan War on the side of the Trojans against the Greeks. As of 2019, the named Neptune trojans are 385571 Otrera (after Otrera, the first Amazonian queen in Greek mythology) and Clete (an Amazon and the attendant to the Amazons' queen Penthesilea, who led the Amazons in the Trojan war).
The amount of high-inclination objects in such a small sample, in which relatively fewer high-inclination Neptune trojans are known due to observational biases, 400+250
−200 Neptune trojans with radii above 40 km in Neptune's L4. This would indicate that large Neptune trojans are 5 to 20 times more abundant than Jupiter trojans, depending on their albedos. There may be relatively fewer smaller Neptune trojans, which could be because these fragment more readily. Large L5 trojans are estimated to be as common as large L4 trojans.
2001 QR322 and 2008 LC18 display significant dynamical instability. This means they could have been captured after planetary migration, but may as well be a long-term member that happens not to be perfectly dynamically stable.
As of February 2020, 29 Neptune trojans are known, of which 24 orbit near the Sun–Neptune L4 Lagrangian point 60° ahead of Neptune, 2008 LC18 , unless otherwise noted.four orbit near Neptune's L5 region 60° behind Neptune, and one orbits on the opposite side of Neptune (L3) but frequently changes location relative to Neptune to L4 and L5. These are listed in the following table. It is constructed from the list of Neptune trojans maintained by the IAU Minor Planet Center and with diameters from Sheppard and Trujillo's paper on
|q ( AU )||Q ( AU )||i (°)||Abs. mag|| Diameter |
|2001 QR322||L4||29.404||31.011||1.3||8.2||~140||2001||First Neptune trojan discovered||MPC|
|2004 KV18||L5||24.553||35.851||13.6||8.9||56||2011||Temporary Neptune trojan||MPC|
|385571 Otrera||2004 UP10||L4||29.318||30.942||1.4||8.8||~100||2004||First Neptune trojan numbered and named||MPC|
|2005 TN53||L4||28.092||32.162||25.0||9.0||~80||2005||First high-inclination trojan discovered||MPC|
|385695 Clete||2005 TO74||L4||28.469||31.771||5.3||8.5||~100||2005||–||MPC|
|(527604) 2007 VL305||L4||28.130||32.028||28.1||8.0||~160||2007||–||MPC|
|2008 LC18||L5||27.365||32.479||27.6||8.4||~100||2008||First L5 trojan discovered||MPC|
|(316179) 2010 EN65||L3||21.109||40.613||19.2||6.9||~200||2010||Jumping trojan||MPC|
|2010 TS191||L4||28.608||31.253||6.6||8.1||~120||2016||Announced on 2016/05/31||MPC|
|2010 TT191||L4||27.913||32.189||4.3||8.0||~130||2016||Announced on 2016/05/31||MPC|
|(530664) 2011 SO277||L4||29.622||30.503||9.6||7.7||~140||2016||Announced on 2016/05/31||MPC|
|(530930) 2011 WG157||L4||29.064||30.878||22.3||7.1||~170||2016||Announced on 2016/05/31||MPC|
|2013 KY18||L5||26.624||34.084||6.6||6.8||~200||2016||Announced on 2016/05/31, stability uncertain||MPC|
|2013 RL124||L4||29.366||30.783||10.1||8.8||~100||2020||Announced on 2020/02/04||MPC|
|2013 TZ187||L4||28.092||32.135||13.1||8.0||~150||2020||Announced on 2020/02/04||MPC|
|2014 QO441||L4||26.961||33.215||18.8||8.3||~130||2014||Most eccentric stable Neptune trojan||MPC|
|2014 RO74||L4||28.426||31.614||29.5||8.4||~120||2020||Announced on 2020/02/04||MPC|
|2014 SC374||L4||27.038||33.060||33.7||8.2||~140||2020||Announced on 2020/02/04||MPC|
|2015 RW277||L4||27.742||32.236||30.8||10.2||~50||2018||Announced on 2018/10/01||MPC|
|2015 VV165||L4||27.513||32.497||16.9||8.8||~90||2018||Announced on 2018/10/01||MPC|
|2015 VW165||L4||28.488||31.488||5.0||8.1||~130||2018||Announced on 2018/10/01||MPC|
|2015 VX165||L4||27.612||32.327||17.2||8.9||~90||2018||Announced on 2018/10/01||MPC|
2005 TN74 and (309239) 2007 RW10 were thought to be Neptune trojans at the time of their discovery, but further observations have disconfirmed their membership. 2005 TN74 is currently thought to be in a 3:5 resonance with Neptune. (309239) 2007 RW10 is currently following a quasi-satellite loop around Neptune.
The Kuiper belt is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles, such as methane, ammonia, and water. The Kuiper belt is home to three objects identified as dwarf planets by the IAU: Pluto, Haumea, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, may have originated in the region.
In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relationship is found between a pair of objects. The physical principle behind orbital resonance is similar in concept to pushing a child on a swing, whereby the orbit and the swing both have a natural frequency, and the body doing the "pushing" will act in periodic repetition to have a cumulative effect on the motion. Orbital resonances greatly enhance the mutual gravitational influence of the bodies. In most cases, this results in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. Under some circumstances, a resonant system can be self-correcting and thus stable. Examples are the 1:2:4 resonance of Jupiter's moons Ganymede, Europa and Io, and the 2:3 resonance between Pluto and Neptune. Unstable resonances with Saturn's inner moons give rise to gaps in the rings of Saturn. The special case of 1:1 resonance between bodies with similar orbital radii causes large solar system bodies to eject most other bodies sharing their orbits; this is part of the much more extensive process of clearing the neighbourhood, an effect that is used in the current definition of a planet.
A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet or dwarf planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (AU).
The Jupiter trojans, commonly called trojan asteroids or simply trojans, are a large group of asteroids that share the planet Jupiter's orbit around the Sun. Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange points: either L4, existing 60° ahead of the planet in its orbit, or L5, 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2 AU.
In planetary astronomy, a centaur is a small Solar System body with either a perihelion or a semi-major axis between those of the outer planets. Centaurs generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one known centaur, 514107 Kaʻepaokaʻawela, which may be in a stable orbit. Centaurs typically exhibit the characteristics of both asteroids and comets. They are named after the mythological centaurs that were a mixture of horse and human. Observational bias toward large objects makes determination of the total centaur population difficult. Estimates for the number of centaurs in the Solar System more than 1 km in diameter range from as low as 44,000 to more than 10,000,000.
2001 QR322 is a minor planet and the first Neptune trojan discovered on 21 August 2001, by the Deep Ecliptic Survey at Cerro Tololo Observatory in Chile. It orbits ahead of Neptune at its L4 Lagrangian point.
Planetary migration occurs when a planet or other body in orbit around a star interacts with a disk of gas or planetesimals, resulting in the alteration of its orbital parameters, especially its semi-major axis. Planetary migration is the most likely explanation for hot Jupiters. The generally accepted theory of planet formation from a protoplanetary disk predicts that such planets cannot form so close to their stars, as there is insufficient mass at such small radii and the temperature is too high to allow the formation of rocky or icy planetesimals.
In astronomy, a resonant trans-Neptunian object is a trans-Neptunian object (TNO) in mean-motion orbital resonance with Neptune. The orbital periods of the resonant objects are in a simple integer relations with the period of Neptune, e.g. 1:2, 2:3, etc. Resonant TNOs can be either part of the main Kuiper belt population, or the more distant scattered disc population.
The scattered disc (or scattered disk) is a distant circumstellar disc in the Solar System that is sparsely populated by icy small solar system bodies, which are a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5×109 km; 2.8×109 mi). These extreme orbits are thought to be the result of gravitational "scattering" by the gas giants, and the objects continue to be subject to perturbation by the planet Neptune.
2005 TN53 is an inclined Neptune trojan leading Neptune's orbit in the outer Solar System, approximately 80 kilometers in diameter. It was first observed on 7 October 2005, by American astronomers Scott Sheppard and Chad Trujillo at Las Campanas Observatory in the Atacama desert of Chile. It was the third such body to be discovered, and the first with a significant orbital inclination, which showed that the population as a whole is very dynamically excited.
In astronomy, a trojan is a small celestial body (mostly asteroids) that shares the orbit of a larger one, remaining in a stable orbit approximately 60° ahead of or behind the main body near one of its Lagrangian points L4 and L5. Trojans can share the orbits of planets or of large moons.
In astronomy, a co-orbital configuration is a configuration of two or more astronomical objects orbiting at the same, or very similar, distance from their primary, i.e. they are in a 1:1 mean-motion resonance..
(309239) 2007 RW10, provisionally known as 2007 RW10, is a temporary quasi-satellite of Neptune. Observed from Neptune, it would appear to go around it during one Neptunian year but it actually orbits the Sun, not Neptune.
The Mars trojans are a group of Trojan objects that share the orbit of the planet Mars around the Sun. They can be found around the two Lagrangian points 60° ahead of and behind Mars. The origin of the Mars trojans is not well understood. One theory suggests that they were primordial objects left over from the formation of Mars that were captured in its Lagrangian points as the Solar System was forming. However, spectral studies of the Mars trojans indicate this may not be the case. Another explanation involves asteroids chaotically wandering into the Mars Lagrangian points later in the Solar System's formation. This is also questionable considering the short dynamical lifetimes of these objects. The spectra of Eureka and two other Mars trojans indicates an olivine-rich composition. Since olivine-rich objects are rare in the asteroid belt it has been suggested that some of the Mars trojans are captured debris from a large orbit-altering impact on Mars when it encountered a planetary embryo.
A cis-Neptunian object is, literally, any astronomical body found within the orbit of Neptune. However, the term is typically used for those distant minor planets other than trans-Neptunian objects: that is, all sub-planetary bodies orbiting the Sun at or within the distance of Neptune, but outside the orbit of Jupiter. This includes the icy minor planets known as centaurs and the Neptune trojans.
The Nicemodel is a scenario for the dynamical evolution of the Solar System. It is named for the location of the Observatoire de la Côte d'Azur — where it was initially developed in 2005 — in Nice, France. It proposes the migration of the giant planets from an initial compact configuration into their present positions, long after the dissipation of the initial protoplanetary disk. In this way, it differs from earlier models of the Solar System's formation. This planetary migration is used in dynamical simulations of the Solar System to explain historical events including the Late Heavy Bombardment of the inner Solar System, the formation of the Oort cloud, and the existence of populations of small Solar System bodies such as the Kuiper belt, the Neptune and Jupiter trojans, and the numerous resonant trans-Neptunian objects dominated by Neptune.
2004 KV18 is an eccentric Neptune trojan trailing Neptune's orbit in the outer Solar System, approximately 70 kilometers in diameter. It was first observed on 24 May 2004, by astronomers at the Mauna Kea Observatories on Hawaii, United States. It was the eighth Neptune trojan identified and the second in Neptune's L5 Lagrangian point.
The five-planet Nice model is a recent variation of the Nice model that begins with five giant planets, the four plus an additional ice giant in a chain of mean-motion resonances.
2011 HM102 is the ninth Neptune trojan discovered. It was first observed on 29 April 2011, during the New Horizons KBO Search (268) using the Magellan II (Clay) Telescope at Las Campanas Observatory in Chile. It has the same orbital period as Neptune and orbits at the L5 Lagrangian point about 60° backwards of Neptune.
The jumping-Jupiter scenario specifies an evolution of giant-planet migration described by the Nice model, in which an ice giant is scattered inward by Saturn and outward by Jupiter, causing their semi-major axes to jump, quickly separating their orbits. The jumping-Jupiter scenario was proposed by Ramon Brasser, Alessandro Morbidelli, Rodney Gomes, Kleomenis Tsiganis, and Harold Levison after their studies revealed that the smooth divergent migration of Jupiter and Saturn resulted in an inner Solar System significantly different from the current Solar System. During this migration secular resonances swept through the inner Solar System exciting the orbits of the terrestrial planets and the asteroids, leaving the planets' orbits too eccentric, and the asteroid belt with too many high-inclination objects. The jumps in the semi-major axes of Jupiter and Saturn described in the jumping-Jupiter scenario can allow these resonances to quickly cross the inner Solar System without altering orbits excessively, although the terrestrial planets remain sensitive to its passage.